Changed localProperties to use ThreadLocal (not DynamicVariable).

The fact that DynamicVariable uses an InheritableThreadLocal
can cause problems where the properties end up being shared
across threads in certain circumstances.
Updated Spark on Mesos documentation.
More updates to Spark on Mesos documentation.
Merge pull request #927 from benh/mesos-docs

Updated Spark on Mesos documentation.
Merge remote-tracking branch 'origin/master' into branch-0.8
Merge pull request #926 from kayousterhout/dynamic

Changed localProperties to use ThreadLocal (not DynamicVariable).
Add developerConnection tag in git
Merge remote-tracking branch 'origin/master' into branch-0.8
Bumping Spark version for RC3